The present invention relates to a Chemical Vapor Deposition (CVD) apparatus for manufacturing semiconductor devices, its driving method, and a method of optimizing a cleaning process for the process chamber. More particularly, the invention relates to in-situ cleaning of a process chamber after processing of semiconductor wafers by using Residual Gas Analyzer Quadrupole Mass-Spectrometer (RGA-QMA).
Generally, the semiconductor device fabrication process is carried out inside a process chamber having certain pre-set process conditions. In particular, when a CVD process is performed on a semiconductor wafer, a layer of material is deposited not only on the wafer, but also on the inner wall of the process chamber tube, and the boat(s) for moving the wafers between the process chamber and a loadlock chamber where the wafers are stored. As these unwanted layers are repeatedly stressed during the loading/unloading of the wafers, particles are released into the chamber that can cause defects on the wafer during the fabrication process.
In order to reduce the causes for defects, PM (Preventive Maintenance) is repeatedly conducted to clean the process tube at regular intervals, but the productivity of semiconductor devices fabrication is decreased due to the interruption of the process line operation.
FIG. 1 illustrates a conventional PM sequence for a general process tube. First, the system is cooled down after carrying out a specific process on semiconductor wafers. After the process chamber is completely cooled, the tubes of the process chamber are taken out one by one so as to carry out wet-etch cleaning of the tubes. The wet-etch generally uses chemicals such as HF group in order to remove polysilicon film or silicon nitride film from the inside of the process tube. Then, the removed tubes are assembled inside the process chamber and a vacuum test is performed. Process Recertification is carried out to see if the process chamber is ready for a new process and if the process conditions for the next process are substantially set up therein.
However, the above PM process represents considerable effort and expense, and takes over 24 hours to complete. Therefore, in order to overcome the problems a plasma etch of using NF3 and CF4 gas is carried out instead of the wet-etch. Alternatively, Thermal Shock Technology is used for removing the layers formed by thermal stress inside the chamber, or the chamber is dry-etched using ClF3, BrF5.
However, even though these technologies are employed, the tubes still must be removed and reassembled and the expense, the labor, and downtime remain as problems.
The present invention is directed to provide a CVD apparatus for manufacturing semiconductor devices wherein a process chamber is equipped with a cleaning gas supply line, a sampling manifold, and a gas analyzer that are used to clean the tubes in situ. As a result, the method of the present invention substantially obviates one or more problems, disadvantages, and limitations of the prior art.
Another object of the present invention is to provide a method of driving the CVD apparatus, wherein a specific process is performed on wafers, and then in-situ cleaning is performed inside a process chamber, after semiconductor wafers are unloaded.
Another object of the present invention is to provide a method of optimizing a cleaning process for a process chamber.
To achieve these and other advantages and in accordance with purpose of the present invention as embodied and broadly described, a CVD apparatus of the present invention includes a process chamber in which a deposition process for manufacturing semiconductor devices is carried out; a plurality of process gas supply lines for supplying process gases to the process chamber; a waste-gas exhaust line for removing the waste-gas from the process chamber; a cleaning-gas supply line for supplying a cleaning gas to the process chamber; a sampling manifold connected to the process chamber for sampling the gas inside therein by using pressure difference; and a gas analyzer for analyzing the sampling gas from the sampling manifold.
Preferably, the process chamber is a Low Pressure Chemical Vapor Deposition (LPCVD) chamber having a sealed outer tube and an inner tube having an open top inside the outer tube. The cleaning gas is ClF3. The cleaning-gas supply line is connected to the inner tube, and the sampling manifold is connected to the outer tube. An orifice is installed in the sampling manifold such that the pressure therein is maintained at the same pressure as in the process chamber. The sampling manifold comprises a first air valve, a second air valve, a first isolation valve, a second isolation valve, a third isolation valve, and a gate valve between the connecting point with the outer tube. A purge-gas supply line is also provided in the sampling manifold. The purge-gas supply line of the sampling manifold is connected to the first air valve and the second air valve from the purge gas supply source, and third and fourth air valves are further provided between them. A Capacitance Manometer (CM) guage and a sampling pump are preferably installed between the first isolation valve and the second isolation valve of the sampling manifold in order to control the first pressure of the sampling manifold.
A scrubber is provided for receiving and cleaning the waste-gas passing through the waste-gas exhaust line, and the gas sampling line.
The gas analyzer is preferably a RGA-QMS (Residual Gas Analyzer-Quadrupole Mass Spectrometer) comprising a mass-analyzer, a turbo pump, and a baking pump, which is preferable in consideration of environmental protection.
The invention is also embodied in a method of driving a CVD apparatus for manufacturing semiconductor devices. The CVD apparatus includes: a process chamber; a plurality of process gas supply lines for supplying process gases into the process chamber; a waste-gas exhaust line for removing the waste-gas from the process chamber after processing; a cleaning-gas supply line for supplying a cleaning gas to the process chamber; a sampling manifold connected to the process chamber; and a gas analyzer for analyzing the sampling gas from the sampling manifold. The method comprises the steps a) sampling the gas from the process chamber; b) outgasing while baking the gas in order to reduce the initial background of the gas analyzer below a certain value; c) conducting a contamination analysis of each of the process gas supply lines; d) performing a specific process for the semiconductor wafers contained in the process chambers, e) unloading the wafers after the above specific process is completed, and exhausting the waste-gas from the process chamber; and f) cleaning the inside of the process chamber by supplying a cleaning gas thereinto.
The sampling manifold and the gas analyzer are continuously purged with a purge gas before conducting the sampling to ensure the precision of the gas analyzer. The contamination analysis for the process gas supply line is performed by passing nitrogen gas through each isolated process gas supply line and checking for leakage. Preferably, the fabrication process of semiconductor wafers is the one for forming a silicon-containing layer on the wafer, and the cleaning process is conducted by introducing nitrogen gas and ClF3 gas as cleaning gases while maintaining uniform pressure inside the process chamber so that the end point of the cleaning process is easily detected.
The method further comprises a step of measuring particles inside the process chamber before and after the cleaning process, and the step of measuring metal/ion contaminants inside the process chamber before and after the cleaning process so as to determine the effectiveness of the cleaning process.
To achieve still another object of the present invention, a method of optimizing the cleaning process for a process chamber, the cleaning process carried out in-situ after a specific process is performed for a wafer placed inside the process chamber, with a cleaning gas supply line for sup plying the cleaning gas into the process chamber, a sampling manifold connected to the process chamber, and a gas analyzer for analyzing the sampling gas from the sampling manifold. The method comprises: a) after performing a specific process on the semiconductor wafer, cleaning the process chamber by supplying a certain amount of nitrogen gas and ClF3 as cleaning gas while maintaining a constant pressure and temperature inside the process chamber until the cleaning end point is detected by the gas analyzer; and b) after performing the same specific process for another semiconductor wafer, cleaning the process chamber by supplying a certain amount of nitrogen gas and ClF3 as cleaning gas, and varying the pressure and the temperature inside the processing chamber until the cleaning end is detected point by the gas analyzer.
Preferably, the end point of the gas analyzer is determined by the intersecting point of amplified traces for an etch gas and the etching byproducts.
According to the present invention, when a specific process is performed on a semiconductor wafer and the cleaning process is carried out inside the process chamber by using ClF3 gas, the mechanism is exactly monitored, and the composition of the cleaning process is optimized to simplify the process and to improve process efficiency.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.